Recovery of tellurium



April 13, 1937. o. c. MARTIN Er AL RECOVERY OF TELLURIUM Filed March lO; 1936 Patented 'Api'. 13', 1937 UNITED STATES PATENT OFFICE 2,076,738 RECOVERY oF TELLURIUM oliver c. Martin, Plainfield, N. J.,` and charles w. Clark, 'Pointe aux Trembles, Quebec, Canada Application March 1o, 1936, serial No. 67,998

i 12 Claims.

5 is more particularly directed to improvements and alternative process steps related to the samev general subject matter as the invention of our co-pending application Ser. No. 711,622, led February 17, 1934, now Patent #2,039,256, entitled Processes of treating renery sludges or shines containing selenium and tellurium, the present invention in its preferred embodiment being directed principally to 'processes for recovery of the tellurium.

J The objects of the invention include the provision of an efficient, economical and reliable process for recovering tellurium from sludges, slimes and slagsor the like materials containing tellurium, and at the same .time if desired, permitting the recovery of precious metals and other metals such as copper, lead and selenium.

Further and more specific objects, features and advantages will more clearly appear from the detailed description given below taken in connection with the accompanying drawing which comprise a vflow sheet schematically illustrating by Way of example one embodiment of apparatus which lmay be used in practicing the invention.

The invention consists in such novel combinations of methods, processes and process steps as may be shown and described in connection with the preferred embodiment of the invention herein disclosed.

In accordance with the process as disclosed in our saidcopending application, the raw sludges or slimes maybe iirst treated as by ltering to remove excess electrolyte, and are then roasted .for example, at 650 to '100 F. with additions of sulphuric acid. This step may be accomplished 40 satisfactorily by continuously feeding the material substantially with the exclusion of ,air y through a multiple herth furnace as indicated 'at I0 in the drawing. This furnace is preferably muiile heatedand the sulphuric acid may be sprayed on to the roasting material at several other selenides to the corresponding sulphates,

the selenium being then liberated from the sele- .nides and volatilized as selenium and selenium dioxide, which is passed out, together with some of the sulphuric acid, through thejurnace ue.

The furnace is preferably operated under a very or less.

slight draft derived from the gases and vaporY formed in the furnace and withdrawn through an `outlet at the top of the furnace as indicated.

Thus substantially no ue dust is lost, as in the oxidizing roast of prior practice. Suiiicientacid 5 is used in the furnace to insure elimination of most of the selenium (in excess of 95%) during the roasting.

The selenium may be recovered from the flue gases in the manner disclosed in our said copending application.

- The roasted slimes from the muille furnace may be subjected to awater leach as at I I, which removes the larger part of the copper as copperV sulphate, and some silver as silver sulphate, from the slimes. In order to remove the silver from the silver sulphate in the leach waters, such waters may be conducted to a precipitator. l2 Where the silver is precipitated from the liquors preferably by means of scrap copper. 'I'he precipitated silver may be charged directly into a Dore furnace I3; The leach liquors, after the silver is precipitated from them, may be sent tov liberators (for example, electrolytic cells), where cathode copper may be deposited out according to the process steps more fully disclosed in our v said copending application.

After the roasted slimes, which contain the tellurium content of the material, are water leached at H, they may be ltered as at I4 and the residue of the filtered slimes may be passed with the precipitated silver to the Dore furnace i3.

'I'he material thus charged into the Dore furf nace may be treated in accordance with the' usual Dore practice and the resulting Dore metal may be sent to a partingl plant. However, since the major part of the selenium is eliminated at the start of the rening process, considerablyv less chemicals, a shorter time of treatment and a smaller Dore furnace will be required, as compared with the usual Dore practice, for a give quantity of Dore metal produced.

The process steps for recovering the tellurium, from the Dore furnace slag will now be described. The slags producedby the uxing of the precious lmetal slimes with soda ash or caustic soda, conthen are preferably crushed to the extent ncces-- 50" sary to form pieces of about one inch in diameter The crushed slag may than be leached with hot water as at I5 so as to. dissolve allV of the soluble salts. The remaining solid material is then separated out as by illter or othei wise, and

the ltrate which contains the tellurium, as sodium tellurite, may be conducted to a precipitation tank as at I6. Sufficient dilute sulphuric acid is mixed with the material in this tank to neu- 5 tralize the alkaline filtrate and to cause the tellurium content to be precipitated as tellurium dioxide. The amount and concentration of the acid should be insufcinet to cause any substantial amount of the tellurium dioxide to be redissolved.

l0 With the tellurium dioxide, compounds of various other metals, such as copper, lead and any remaining selenium, will also be precipitated andit is therefore necessary to further treat the precipitate to extract the tellurium in a pure state.

Heretofore the usual method of treating such precipitate has been to dissolve the same inga solution of sodium hydroxide and reprecipitate with sulphuric acid, this procedure being repeated several times until a pure tellurium dioxide was produced. The pure tellurium dioxide was then mixed with some reducing agent such as flour, starch or charcoal, then heated in a crucible until molten and ready to be cast into bars of como mercially pure tellurium. However, with this a process as heretofore used, it was very diillcult to eiilciently remove all of the impurities fromv the tellurium and some wastage of other recoverable materials was involved.

According to our present invention, the precipitates and leachwaters of the tank I6 may be conducted to a lter H or other apparatus for separating the precipitates from the leach waters. Solutions from this step may be acidifled after ltration and gassed with SO2 to recover any selenium present. The solution, after separation of selenium, may then be sent to waste. 'I'he 4precipitates including the tellurium dioxide, and any copper, lead and/or selenium present'in precipitated forms may be then mixed with hot con- Qcentrated sulphuric acid as at IB in sufficient amounts. to provide a thickmud-like mixture,

slurry or sludge.

'I'he slurry may be then charged into a reverberatory furnace as at I9, 'heated to a temper- 4 ature in the neighborhood of from 700 to 800 F., the mixture preferably remaining in the furnace until it is dry. The material should be roasted until all i'ree sulphuric acid has been fumed off,

otherwise some of the tellurium will be dissolved "q in the water leach. Thisremoves most of the remaining troublesome amounts of selenium byY volatilization. -The selenium thus removed may be conducted to apparatus for recovering various puried forms of selenium, such for example as disclosed in our said copending application. Other materials remaining in the reverberatory furnace `such as the copper and lead, are converted into their corresponding sulphates and 60 these, together with the tellurium dioxide, are water leached and put through a filter or other separating means as at 20 whereby the copper, as copper sulphate, may be removed with the leach waters` and conveyed to the copper liberators 65 above mentioned.

'I'he residue from this leach may now be leached 1 as indicated at 2 I, for example with a 20% solution of sulphuric acid to dissolve the tellurium dioxide. Sodium sulphite may now be added to 70 the tellurium bearing solution, the acid and the sodum sulphite being made suillcient to precipitate a very small amount of the tellurium as metallic tellurium. During this operation the solution may be agitated vigorously as by a suitable .75 agitator 22 in order that the precipitated Itellu- 2,o7e,'irss i rium may cement out any traces of selenium that remain in the solution.

The solution may now be filtered as at 23 or otherwise treated to separate the small amount of precipitated tellurium, together with the selenium cemented out therewith and the lead sulphate which may if desired be returned to one or the other of the above described furnaces. The ltrate comprising tellurium dioxide solution may the sulphuric acid contained, to hydrochloric acid.

Thereupon the hydrochloric acid tellurium solution may be gassed with sufficient sulphur dioxide to precipiate substantially all of the tellurium as metallic tellurium, which may be separated out as by a filter 25. The tel1urium.may be then washed as at 26,.melted in a crucibley as at 21, and thereafter cast into bars of commercial tellurium.

While the invention has been described in detail with respect to particular preferred examples, it will .be understood by those skilled in the art after understanding the invention, that various changes andfurther modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in` the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. Process of recovering tellurium from materials of the nature of alkaline slags containing a tellurium compound together with other substances including copper, lead and/or selenium, which comprises water leaching said material,

mixing suilcient ldilute sulphuric acid with the resulting leach waters to form precipitates including an oxide of tellurium, separating the precipitates from-the resulting liquid, applying hot concentrated sulphuric acid to the precipitates to form a mud-like mixture, heating said mixture to a temperature suiiicient to drive off a substantial part of any selenium present, and to leave a dry mixture containing sulphates and the oxide of tellurium, removing the soluble sulphate by water leaching the latter mixture, then removing the oxide of tellurium by applying a liquid to dissolve the same, and applying reagent material to the oxide of tellurium solution to precipitate metallic tellurium.

2. Process of recovering tellurium from materials of the nature of alkaline slags containing a tellurium compound together with other substances including copper, lead and/or selenium, which comprises Water leaching said material, mixing sufficient dilute sulphuric acid with the resulting leach waters to form precipitates including an oxide of tellurium, separating the precipitates from the resulting liquid, applying hot concentrated lsulphuric acid to the precipitates to form a mud-like mixture, heating said mixture to a temperature suflicient to drive oil a substantial part of any selenium present, and to leave a dry mixture containing sulphates and the oxide of tellurium, and subjecting said mixture to further-treatment to obtain-metallic tellurium therefrom.

3. Process of recovering tellurium from matevture to a temperature suflcient to drive oi a substantial part of any-selenium present, and tol leave a dry mixture containing sulphates and an Y oxide of tellurium, removing the soluble sulphate by water leaching the latter mixture, removing the oxide of tellurium by applying a liquid to dissolve the same, and applying reducing agent to the oxide of tellurium solutionto precipitate metallic tellurium.

4. Process of recovering tellurium from material containing an oxide of tellurium together `with small amounts of selenium, which comprises applying to said material dilute sulphuric acid and sodium sulphite, agitating the resulting mixture, the quantities of said acid and sulphite being such as to precipitate a small amount of tellurium sufcient to cementI out the selenium content of the material, then separating the precipitates includingl the selenium from said mixure, and subjecting said mixture to further treatment to obtain metallic tellurium therefrom.

5. Process of recovering tellurium from material containing an oxide of tellurium together with small ainounts of sellenium, which comprises applying to said material dilute sulphuric acid and sodium sulphite, agitating the resulting mixture, whereby a small amount of tellurium is precipitated sufficient to 'cement out the selenium content of the material, then separating the precipitates and any other solids from said mixture, adding salt to the remaining liquid to form a hydrochloric acid solution, and adding a reducing agent to said solution to precipitate the metallic tellurium therefrom.

6. The process steps of recovering tellurium from a sulphuric acid solution containing an oxide of tellurium, which comprise adding to said solution sufcient salt to convert said acid to hydrochloric acid, and, adding a reducing agent for precipitating metallic tellurium from the solution.

40 7. The process steps of recovering ltellurium from a sulphuric acid solution containing an oxide of tellurium, which comprise adding to said solution suflicient salt to convert said acid to hydrochloric acid, and precipitating metallic tel lurium from thevsolution by the use of sulphur dioxide gas.

8. Process of recovering tellurium from materials containing a tellurium compound together with other substances including copper, lead and/or selenium, which includes the steps of treating the material with sulphuric acid in a manner to remove .the larger part of any selenium present, removing any soluble sulphates formed, then applying to the residue dilute sulphuric acid and sodium sulphite,agitating the resulting mixture, the quantities of said dilute acid and sulphite being such as to precipitate a small amount of tellurium suicient to cement out the remaining Y selenium content of the material, then `sepa'ating the precipitates including the latter selenium from the mixture, and adding reagent material to the remaining liquid for precipitating the metallic tellurium.

9. Process of recovering tellurium from materials containing tellurium and selenium which comprises subjecting the material while in a solution of sulphuric acid, to a treatment for removal of the selenium, then adding to said solution suiiicient salt to convert saidacid to hydrochloric acid, and adding a reducing agent for precipitating metallic tellurium.

10. Process of recovering tellurium from material containing an oxide of telluriumtogether with small amounts of selenium, which comprises applying to said material dilute sulphuric acid and a reducing agent, agitating the resulting mixture, the quantities of said acid and reducing agent being such as t0 precipitate a small amount of tellurium sufficient to cement out the selenium content of the material, then separating the precipitates including the selenium from said mixture, and subjecting said mixture to further treatment to obtain metallic tellurium therefrom.

1l. Process of recovering tellurium from materials of the nature of alkaline slags containing. a tellurium compound together with other substances including copper, lead and/or selenium, which comprises water leaching said material, mixing suilcient dilute sulphuric acid with the resulting leach Waters to form precipitates including an oxide of tellurium, separating theprecipitates from the resulting liquid, recovering any selenium present in said liquid, and subjecting the precipitates to further treatment to recover tellurium therefrom.

12. Process of recovering tellurium from matef rials of the nature of alkaline slags containing a tellurium compound together with other substances including copper, lead and/or selenium, which comprises water leaching said material,

mixing suicient dilute sulphuric acid with the resulting leach waters to form precipitates including an oxide of tellurium, separating the precipitates from the resulting liquid, whereby any substantial quantities of selenium present are eliminated with such liquid, heating the precipitates with sulphuric acid for the further elimination of selenium, and subjecting the remaining material to further treatment to recover tellurium therefrom. v

OLIVER c. MARTIN. yCHARLES w. CLARK. 

